Kev's "Cobble Together a Good 3000 PL Preamp" thread...

[laatsch55]

Good luck Mr. Jer....

 

[jbeckva]

Well since I have the one I am going to swap in out of it's cage, I figure let's go one step further and recap here as well.

I have the parts for the big 470's ready to order, but ... I know we generally don't want those ceramic pieces of crap, right? Soo.. .01uf I believe... who's got a good non ceramic sub for 'em?

 

[laatsch55]

Ceramics OK in a power supply I think Jer. The same poly's we use on our bridges would work Jer. The 400volt/,01's

 

[jbeckva]

Works for me.. order sent...

I'll mod the resistors to drop it down to 16 tomorrow anyway tho... might get "lucky" there, and I can yank the board back out when the new caps come next week.

 

[laatsch55]

Hookay...

 

[kevin]

O man..... Krystal's birthday is Monday...... Sure glad I aint giving her a pre-amp.....LMAO.... I'll give her a CD player Jer... Can I tell her she is getting PRE-AMP for Christmas ??????

 

[jbeckva]

O man..... Krystal's birthday is Monday...... Sure glad I aint giving her a pre-amp.....LMAO.... I'll give her a CD player Jer... Can I tell her she is getting PRE-AMP for Christmas ??????

Hmm.. how about I just finish it up and ship it out.. TODAY???

Obviously this doesn't do it justice, but I will tell you I am tempted to send you MINE and keep this one, LOL. Nah I wouldn't do that to ya, Kev. Anywhoo... so I figured out where the issue was... the old saying "walks like a duck, talks like a duck, must BE a duck" applied - Damn if those standoffs were not LOOSE, and those provide the main chassis ground to the power supply!

I knew I wasn't nuts... this pre DID sound good a few posts back, so it was likely that the ground contact was "just" enough.. but then when it broke contact, that's where the buzz came back.

I will tighten the shit out of 'em when I get it back together tonight, then after a few hours of listening OFF IT GOES!!

<iframe width="640" height="360" src="//www.youtube.com/embed/SjU2q_j579c?feature=player_detailpage" frameborder="0" allowfullscreen></iframe>

 

[jbeckva]

ps... If you notice right around 0:43 I glance down at the UPS.. That's a 1500VA UPS telling me I'm "pushing it", LOL...

 

[laatsch55]

Infected Mushroom!!! Perfect....

 

[laatsch55]

Good job tamin the beast Jer..

 

[CASSETTE DECK]

I have a variant of this circuit

I have added a schematic to post 99 for ease of comparison between schematics.

I would also post the schematic into another thread. Any suggestions?

 

[laatsch55]

CD, let's start a new sub-forum----"Useful Circuits" whadda ya think?

 

[CASSETTE DECK]

CD, let's start a new sub-forum----"Useful Circuits" whadda ya think?

It's certainly true that the DIY and other "how to make a monster" tales section is already very large and it doesn't take long for threads to get "buried".

Given the importance of good electronic circuit designs for what we do here at Phoenix Audio, I think it's a great idea to start a new sub-forum similar to the WOPL archives.

 

[laatsch55]

You got it..

 

[CASSETTE DECK]

You got it..

Great stuff! Thank You.

Things just keep getting better here all the time!

 

[laatsch55]

We aim to please...

 

[jbeckva]

Good job tamin the beast Jer..

Thanks Lee

My only gripe (and really it's not too bad) is the SN ratio is still not where I'd like it to be. It's pure "hiss" so I am assuming the power supply issue is probably not part of it. Again bear in mind I have D9's with that 108db SPL rating, and it's only with the volume high enough to be classified as "pretty dern loud".

Now there is a tech bulletin addressing it. It involves changing R150 from 20K to 9K, and R156 from 1.1K to 1.8K. The tech bulletin claims a 6 db increase in SN ratio.

I'm thinking I should do it, but wanted to check with Joe as far as further mods. Joe let me know if you do have all of the schematic needed. I can also scan the bulletin in and send that...

 

[Gepetto]

Thanks Lee

My only gripe (and really it's not too bad) is the SN ratio is still not where I'd like it to be. It's pure "hiss" so I am assuming the power supply issue is probably not part of it. Again bear in mind I have D9's with that 108db SPL rating, and it's only with the volume high enough to be classified as "pretty dern loud".

Now there is a tech bulletin addressing it. It involves changing R150 from 20K to 9K, and R156 from 1.1K to 1.8K. The tech bulletin claims a 6 db increase in SN ratio.

I'm thinking I should do it, but wanted to check with Joe as far as further mods. Joe let me know if you do have all of the schematic needed. I can also scan the bulletin in and send that...

Hi Jer
I only have the jpgs you sent me of portions we were working on. These schematics are about the worst I have ever seen for legibility, at least in the service manual that I have.

 

[jbeckva]

Hi Jer
I only have the jpgs you sent me of portions we were working on. These schematics are about the worst I have ever seen for legibility, at least in the service manual that I have.

I'll send you the service bulletin in a few. FWIW, R150 is the input (Rin) while R156 is feedback (Rf) I believe.. Well, sorta.. R150 is back a bit from the volume pot, but also first in serial with the actual selected input signal. R156 seems part of a divider from the typical Rf resistor (on the input side of it), with a 100 uF cap to ground.

Let me get it to you in a few.. heheh

 

[jbeckva]

BTW.. got 'er all back together, and up on the stack. Just wonderful sound right now...